Notes on the effect of grain crushing on the granular soil behaviour

Two granular materials — alluvial quartzy Zbraslav sand and granular silica gel — were tested with the intention to demonstrate the effect of grain crushing. Stepwise transformation of the compression curve produced by progressive grain crushing was observed. Due to grain crushing, shear strength envelope became nonlinear, and the behaviour was no more physically isomorphous. The shear stress–strain diagrams acquire a typical wavy (garland-like) form, induced by periodic softening and hardening of the soil response. The intensity of grain crushing depends (in addition to stress level, grain resistance and time) on the shear path. In the crushing phase, initial porosity and angularity play a secondary role. Many other behavioural features common with granular soils (like increase in dilatancy with density and grain size) are suppressed. Grain crushing thus produces a qualitatively different feature of geomaterial behaviour with grave practical consequences (dense sand, e.g. starts to behave like loose).